Explain the 'ABO blood grouping system' in humans. OR Describe the structure and function of the 'human nephron'.

ABO Blood Grouping System in Humans

The ABO blood grouping system is the most important classification of human blood based on the presence or absence of specific antigens (agglutinogens) on the surface of red blood cells (RBCs) and corresponding antibodies (agglutinins) in the plasma. This system is genetically determined and plays a crucial role in blood transfusion compatibility.

Types of Blood Groups

There are four main blood groups in the ABO system:

1. Blood Group A

   • Antigen: A
   • Antibody: Anti-B
   • Genotype: IAIA or IAi
   • Can receive blood from: A and O
   • Can donate blood to: A and AB

2. Blood Group B

   • Antigen: B
   • Antibody: Anti-A
   • Genotype: IBIB or IBi
   • Can receive blood from: B and O
   • Can donate blood to: B and AB

3. Blood Group AB

   • Antigen: Both A and B
   • Antibody: None
   • Genotype: IAIB
   • Can receive blood from: A, B, AB, and O (universal recipient)
   • Can donate blood to: AB only

4. Blood Group O

   • Antigen: None
   • Antibody: Both Anti-A and Anti-B
   • Genotype: ii
   • Can receive blood from: O only
   • Can donate blood to: A, B, AB, and O (universal donor)

Genetic Basis

• The ABO blood group is controlled by a single gene with three alleles: IA (A antigen), IB (B antigen), and i (no antigen).
• IA and IB are codominant, while i is recessive.
• For example:
  • IAIA or IAi → Blood Group A
  • IBIB or IBi → Blood Group B
  • IAIB → Blood Group AB
  • ii → Blood Group O

Importance in Transfusion

• If incompatible blood is transfused, the recipient’s antibodies attack the donor’s RBCs, causing agglutination (clumping) and hemolysis (destruction of RBCs), which can be fatal.
• Thus, blood typing is essential before transfusion to ensure compatibility.

Rh Factor

• The ABO system is often combined with the Rh factor (positive or negative), making eight blood groups in total (e.g., A+, B-, AB+, O-).

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OR

Structure and Function of the Human Nephron

The nephron is the functional unit of the kidney responsible for filtering blood and producing urine. Each kidney contains about 1 million nephrons, which work together to maintain homeostasis by regulating water, electrolyte balance, and waste removal.

Structure of the Nephron

The nephron consists of two main parts:

1. Renal Corpuscle

   • Glomerulus: A network of capillaries where filtration occurs.
   • Bowman’s Capsule: A cup-shaped structure that collects the filtrate (glomerular filtrate).

2. Renal Tubule

   • Proximal Convoluted Tubule (PCT): Highly coiled and lined with microvilli to maximize reabsorption of water, glucose, amino acids, and ions.
   • Loop of Henle: A U-shaped tube that plays a key role in concentrating urine by creating a osmotic gradient (descending limb reabsorbs water; ascending limb reabsorbs salts).
   • Distal Convoluted Tubule (DCT): Selectively reabsorbs ions (e.g., Na⁺, Ca²⁺) and secretes waste products (e.g., H⁺, K⁺, urea).
   • Collecting Duct: Merges filtrate from multiple nephrons, fine-tunes water and salt balance under the influence of ADH (antidiuretic hormone) and aldosterone.

Blood Supply

• Afferent Arteriole: Brings blood into the glomerulus under high pressure for filtration.
• Efferent Arteriole: Carries filtered blood away, leading to the peritubular capillaries for reabsorption.

Functions of the Nephron

1. Filtration
   • Occurs in